248 F. C. SCHRADER GEOLOGICAL SECTION IN NORTHERN ALASKA 



Where best observed on the Anaktoovuk, the beds strike nearly east and 

 west and dip south at an angle of 80 degrees, but the prevailing dip of 

 the series, however,' is probably north. The series has been somewhat 

 folded and slightly faulted, and it is cut by a pronounced system of joint- 

 ing or sheeting along planes approximately horizontal. 



Age.— On fossil evidence, the series is assigned to the Upper Cretaceous 

 by Doctor Stanton, who has identified the following forms : 



Inoceramus, a large species. TeUina, two species. 



Astarte, numerous. Sillgua. 



Nucula, numerous specimens. Modiola. 



Avicula. Scaphites. 



Pninnculus, several specimens. Hammonia. 

 Thracia. 



UPPER CRETACEOUS ON THE KOYVKVK 



To the south of the Endicott range and south of the limits of the 

 section in the Koyukuk region, Upper Cretaceous has also been found. 

 Of the collection made here by the writer. Doctor Stanton reports the 

 following forms and refers the beds to about the same horizon as the 

 early Chico : 



Ostrea. Lucina. 



Anomya. Trigonia cf. T. lexna Gabb. 



Mytilus. Corhula. 



J^ectunculus cf. P. veaichii Gabb. Actseonella cf. A. oviformw Gabb. 



Opir f 



Tertiary — Colville Series 



This series of Tertiary terranes succeeds the Upper Cretaceous or 

 Nanushuk series on the north, forming a flat tundra country or coastal 

 plane. It extends from some distance above the mouth of the Anak- 

 toovuk 100 miles northeastward to the Arctic coast. The inland edge 

 of the coastal plain has an elevation of about 800 feet, from which, with 

 very gradual slope, the surface descends approximately to sealevel at the 

 coast. The series consists principally of heavy bedded, partially con- 

 solidated silts or mud rock, with intercalated harder layers of soft sand- 

 stone, limestone, shale, lignite, and unconsolidated silts (see plate 43). 

 The sediments are conspicuously derived from the preceding Cretaceous 

 formations and the Paleozoics of the Endicott range. So far as observed 

 during the past season, the series is separable into two parts — Oligocene 

 and Pliocene. The portion assigned to the Oligocene is best exposed 

 along the Colville in the region of the mouth of the Anaktoovuk. Here 



